Purification of unsaturated compounds



Patented Aug. 13, 1940 Alger L. Ward, Drexel Hill, Pa assignor to The United Gas In: tion of Pennsylv provement Company, a corporaania,

No Drawing. Application October 22, 1937, Serial No. 170,508

I 6Claims.

This invention pertains generally to the purification of compounds, and pertains particularly to the purification of hydrocarbons such as cyclopentadiene.

In many of the processes for the production of 1 hydrocarbons of various boiling points are prohese are various double bonded For instance, when petroleum oil is used in the quantities of butadiene 1,3, (B. P. 4.5 0.), isoprene (B. P. 34 C.) cyclopentadiene (B. P. 40 0.), pentadiene 1,3 (B.- P. 43 C.), styrene (B. P.

145 0.), and indene (B. P. 182 0.).

There are also present appreciable quantities of aromatic substances such as benzene (B. P. 79.6 toluene (B. P. 110.5 0.), ortho, meta and para xylene (B. P. 144 c., 139 0., and 138 0. re-

oven gas, considerable quantities of CS2 may be present.

There are usually also present certain quantities of olefins and parafllns.

These materials are um and low temperature diene from substances such I have found that cyclopentadiene, as distinguished from isoprene and piperylene, is characterized by the ease with which it may be polymermay merization of the dicyclopentadiene formed from it.

cyclopentadiene.

Although little is known about the polymerizaparatus clopentadiene and secondly because the presence of catalysts tends to result in the formation of molecules larger than the dimer and these higher molecular weight polymers do not depolymerim readily to give cyclopentadiene.

I have discovered that cyclopentadiene may be readily and rapidly polymerized in the presence or isoprene, piperylene and other hydrocarbons without at the, sametime polymerizing significant proportions of such other materials. This may be accomplished by subjecting the crude cy clopentadiene under superatmospheric pressure to an elevated temperature preferably considerably above the initial boiling point of the cyclopentadiene mixture. By initial boiling point" is meant the initial boiling point of the monomeric mixture at atmospheric pressure and this will be so used hereinafter.

Furthermore, I have found that the depolymerization of the dicyclopentadiene can be selective so that the small quantities of the other polymers formed incidental to the polymerization step are not depolymerized to low boiling monomers that taminate the cyclopentadiene formed by the depolymerization of the dicyclopentadiene.

first step of my invention, any means known in the art may be employed for temperature of, and pressure on, the cyclopentadiene mixture for the purpose of selectively polymerizing the cyclopentadiene to dicyclopentadiene.

I find, for instance, that a closed vessel, such as an autoclave, is very suitable for this purpose. In this case the initial pressure is a function of, and is deternnned by, the temperature. As the polymerization progresses, the pressure for a given temperature decreases due to the formation of higher boiling polymers.

However, independently of how the pressure is applied, I find that the reaction cyc1opentadienez dicyclopentadiene will proceed to the right with reasonable rapidity if a temperature considerably in excess of 40 C high a rate of reaction toward the left, the temperature usually should not exceed 170 C.

temperature in the neighborhood of and satisfactory. The term in the neighborhood of 100 C. is intended to include 100 C. and will be so employed in the aims.

It will be obvious that any other type of apmay be substituted whether adapted to carry out this polymerization step in batch, semicontinuously, continuously or otherwise.

I find it advantageous, however, particularly from the standpoint of avoiding the formation of dicyclopentadiene diperoxide or other oxygenated compounds to carry out the polymerization in a system at least substantially free from oxygen. This may be accomplished in most instances at least by purging the system with an inert gas, such as nitrogen.

I also find it advantageous to maintain at least the larger part of the reacting material in the liquid phase. This may be accomplished either by mechanical regulation of pressure, by limiting the vapor space above the liquid, or otherwise, as desired.

At the end of the polymerization step (during which cyclopentadiene is polymerized to dicyclopentadiene) the dicyclopentadiene may be separated from the lower boiling materials by any vention.

suitable means such as distillation at low pressure to purify the dicyclopentadiene.

I find the dicyclopentadi purity may be obtained tion at low pressure for this depolymerization of the dicyclopentadiene is thus avoided during the distillation, particularly if the pot temperatures are kept low and prefer are not permitted to rise above appi'oxima 140 C.

Having separated the vdicyclopentariiene from the other materials present, the final step comprises depolymerizing the dicyclopentadiene to cyclopentadiene. as this al is more stable and easier to handle and transport in the dicyclopentadiene form, it may be desirable to delay the third step until the cyclopentadiene is required for use.

Depolymerization may be conveniently accomplished by dicyclopentadiene at or near its boiling erably with provision for removin pentadiene vapors as rapidly as they are f The conventional retort and condenser are suitable for this p and particularly when provision is made for condensing and refluxing any dlcyclopentadiene vapors that may be formed.

Appropriate apparatus of wide variety will suggest itself to persons skilled in the art upon becoming familiar with this invention.

The following example will The data, however must be interpreted in light of exact methods of analysis for determining cycloisoprene frequently occur. Therefore, were obtained by the best analytical methods known, they are nevertheless not represen absolutely exact.

To show the completeness and selectivity of the polymerization, 350 milliliters (252 grams) of a cyclopentadiene fraction containing 31.5% cyclopentadiene and 47% other diene were heated in a closed autoclave for 24 hours at a temperature of approximately 92 C. The initial pressure developed was 55 pounds per square inch (gauge).

99.9% of the cyclopentadiene was polymerized of which 95.5% was dicyclopentadiene and the rest higher polymers.

Only 6.6% of the other polymerized.

The above example clearly illustrates not only the high selectivity of the process for polymerizing cyclopentadiene in preference to other dienes, but also the high selectivity of the process for polymerizing cyclopentadiene to dicyclopentato higher polymers thereof.

I have found that total polydiene formation increases as the time or temperature of the polymerization increases and as the percentage of cyclopentadiene in the original charge decreases. 0n the other hand, after removal of the dicyclopentadiene formed as above, further heating appears to cause only slight further polymerization of the other dienes present. This indicates that the presence of cyclopentadiene or dicyclopentadiene influences the polymerization of the other dienes, notwithstanding the fact that under the conditions disclosed a substantial portion of the ot r dienes are not polymerized even in the presence of cyclopentadiene. However, the subject is complicated by many factors including the fact that cyclopentadiene and dicyclopentadiene dienes present were the fact that there are at present no 8,911,088 will form polycycldpentadiene on heating without the application 01' pressure.

I find that heating for a period of 24 hours at a temperature in the neighborhood of C. is very suitable.

The separationof dicyclopentadiene from the mixture is results. The purpose of low pressure distillation is, or course, to reduce the required still pot temperatures, thus avoiding depolymerizationoi dl-' is suitable for present-inproduces a highly purified dicyclopentadiene.

Another important application of the invention is its use for the removal of residual unpolymerized cyclopentadiene from the unpolymerized .materiai remaining after the separation oi dicyclopentadiene as set forth above.

Since-this unpolymerized portion usually contains isoprene andplperylene which it is also desired to recover, the removal 01' all traces of the third component, cyclopentadiene, important.

This may be accomplished the cycle of herewith.

It is to be understood that the above particular description is by way of illustration and that changes. omissions, additions, substitutions and/ or modifications may be made within the claims withou the invention, which is intended to be limited only as required by the prior art.

I claim:

subjecting said mixture in liquid phase to superatmospheric pressure and to elevatedtemperature between 40 C. and C. to selectively dimerise the above degree of purity becomes I :cyclopentadiene-is separated from cyclopentadiene to dicyclopentadiene, said superatmospheric pressure being sufllcient said liquid phase.

2. In a process for selectively separating cyclopentadiene from a cyclopentadiene containing traction obtained by distillation mixture in liquid phase in the substantial absence of oxygen to pressure and" to temperature conditionssubstantiaily above 40 C. but substantially below 170' C.

to convert cyclopentadiene to dicyclopentadiene. said superatmosphel'ic pressure being sumcient to maintain said liquid phase.

5. In a process for all! below 170 C. for a time suillcient to selectively dimerize at least the preponderant part oi said 1 cyclopentadiene to dicyciopentadiene, said superatmospheric pressure ,rbeingsumcient to maintain at least the larger liquid phase.

6. In a process for selectively separating cyclopentadiene from a mixture con g other heat polymerizable diene material or similar boiling point wherein said cyclopentadiene is selectively converted to dicyclopentadiene, wherein said diunpolymerized wherein said separated being sumcient to maintain at least the larger part of said mixture in theliquid phase.

s am nswsan.

to maintain part of said materials in the 

